The present invention relates to a blower.
Reducing equipment in size using electronic devices has prompted the use of high-density electrical circuits. Since the density of heat produced by electronic equipment increases with increasing density of electronic devices in it, axial-flow blowers or oblique-flow blowers are used to cool electronic equipment.
As shown in FIG. 11, in a conventional blower, an annular wall 2 is formed away from the end of a blade of an axial-flow fan 1, which rotates about a shaft 4, thus causing an air flow 5 from the suction side to the discharge side when a motor 3 is energized, that is, the blower is in operation.
When the blower is in operation, however, the velocity of the air flow increases on the back pressure side at the blade end, so that under the influence of secondary flows between blades, a low-energy region occurs on the blade trailing edge side, where the velocity is converted to pressure energy.
In the low-energy region, energy loss is significant and air flow easily separates from blade surfaces, over which vortices occur, thus increasing turbulent flow noise. Thus the region poses a problem of an increase in noise level and a deterioration in static pressure-flow rate characteristic (hereinafter referred to as the P-Q characteristic).
The phenomenon mentioned above is frequently observed, especially when a fan exhibits stall conditions because large leakage vortices occur at the end of a blade under the action of flow resistance (system impedance) on the discharge side.
U.S. Pat. No. 5,707,205, previously obtained by the applicant of the present invention, discloses that by sucking laminar air flow inside an annular wall through a slit therein when a blower is in operation, a blower inhibits leakage vortices and rotation stall from occurring at the end of a blade to improve the P-Q characteristic and reduce noise.
PCT-based Japanese Pat. Laid-Open No. 6-508319 and U.S. Pat. No. 5,292,088 disclose that a blower is arranged so that vortices of air flowing through a plurality of rings, spaced apart from each other around an axial-flow fan, increase the air flow rate.
U.S. Pat. No. 5,407,324 discloses that a blower is arranged to make it possible for air to flow inside and outside a housing by inclining to the direction of air flow the internal perimeter of a plurality of annular plates, stacked around an axial-flow fan.
However, common blowers for personal computers and workstations, which are made rectangular with standardized dimensions to reduce their costs, have external dimensions of 60 mm square to 92 mm square. Thus it is not desired that a blower be significantly changed into a round shape by, for example, making annular plates 71 to 75, forming the annular wall 2, circular as shown in FIG. 12.
U.S. Pat. No. 5,707,205 also discloses a blower whose annular wall 2 is shaped so that its sections corresponding to the middle of the upper, lower, right, and left sides of a rectangular casing body 15 are flush with the casing body 15 as shown in FIGS. 13a and 13b. However, only making the contour of the annular wall rectangular as shown in FIGS. 13a and 13b causes the effect of sucking laminar air flow inside the annular wall through each slit 6 to be slightly lessened, compared with an annular wall which has a round contour as shown in FIG. 12. Thus the effect of improving the P-Q characteristic and reducing noise cannot fully be provided. The casing body described by U.S. Pat. No. 5,707,205 also has a problem of low mechanical strength and the like, because the sides of the annular wall are thinner than the other sections.
Every blower mentioned above improves a fan characteristic by sucking air around a fan. The applications only describe the arrangement of rings (annular plates) around a fan, not the shape of the fan. To fully exhibit the characteristic of a fan, its shape must be devised.
A method has generally been used which predicts the performance of a fan or determines the three-dimensional shape of a fan appropriate for use conditions by cutting a fan blade through the surfaces of cylinders concentric with the axis of rotation of the fan, developing the surfaces, converting a fan blade into a plane infinite straight-line series, and applying to the series a straight-line airfoil system theory suggested for aircraft and the like.
However, a problem with the method is that the actual performance of a fan becomes lower than that predicted by calculations under the influence of leakage vortices at the ends of blades when flow resistance higher than a given level acts on the blower.
To solve this problem by modifying the shape of the end of a blade, some fans, including one disclosed in Japanese Patent Application Laid-Open No. 6-307396, are arranged so that aerodynamic performance is improved and noise is reduced by positioning the cross-sectional section at the end of an outer blade of the fan on the leading edge side and providing an upwardly curved one-sided curved section and an arcuate section following the one-sided curved section only on the pressure surface side.
Some blowers, including one disclosed in Japanese Patent Application Laid-Open No. 8-121391, are arranged so that aerodynamic noise is reduced by curving the periphery of a blade.
Some hydraulic apparatuses, including one disclosed in Japanese Patent Application Laid-Open No. 8-284884, are arranged so that by cutting the back side of the end of a moving blade a given height from the tip and forming a thin-walled section of a constant thickness on the back side, fluid leakage from a tip clearance is reduced, thus improving the efficiency of an axial-flow blower.
However, if the above-described fan shapes according to prior art, which assumes that no air flows in from outside an annular wall, are applied to an arrangement where air is sucked from outside an annular wall, no satisfactory performance is exhibited.
Although U.S. Pat. No. 5,407,324 discloses an arrangement of the rings, the arrangement is not acceptable in terms of mass productivity, strength, and accuracy.
It is an object of the present invention to provide a blower which exhibits an improved P-Q characteristic and reduces noise as a blower in FIG. 12 whose annular wall has a circular contour even when substituted for a conventional rectangular blower and which has practically necessary strength.
It is another object of the present invention to optimize the shape of a fan blade and that of an annular wall of a blower which sucks air inside the wall through slits provided therein to improve aerodynamic performance and strength and reduce cost by increasing mass productivity.
First of all, an annular wall of a blower according to the present invention is described which is contoured in a non-circular shape including a rectangular shape. The present invention provides a blower characterized in that an annular wall is formed away from the ends of fan blades, and slits passing from the circular inner perimeter to the non-circular outer perimeter of the annular wall are provided in sections of the wall which are opposite to the ends of fan blades, whereby the flow rate of air flowing inside the annular wall through the slits is constant around the annular wall, although the distance between the inner perimeter and the outer perimeter varies with locations in the annular wall.
The blower is also characterized in that the flow rate of air flowing inside the annular wall through the slits is made constant all around the annular wall by continuously changing the width of the slits, w, according to the radial length between the inner perimeter and the outer perimeter of the annular wall, L, so that the condition represented by the following equation or its close condition is met:
w3/L=constant.
The blower is also characterized in that the flow rate of air flowing inside the annular wall through the slits is made constant all around the annular wall by changing the width of the slits, w, and the number of slits in the direction of the axis of rotation, n (n is a positive integer), according to L, so that the condition represented by the following equation or its close condition is met:
nxc2x7w3/L=constant.
Specifically, the annular wall with the slits is arranged by stacking a plurality of annular plates in the direction of the axis of rotation of a fan, the annular plates being separated from each other.
More specifically, the present invention provides a blower which sucks air inside an annular wall through slits as a fan rotates, the annular wall being formed away from the ends of fan blades, the outer peripheral sections of the annular wall which correspond to the ends of fan blades being formed to be planar and substantially flush with a rectangular casing body at the middle of upper, lower, right, and left sides of the body, and slits, passing from the circular inner perimeter to the non-circular outer perimeter of the annular wall, being provided in sections of the wall which are opposite to the ends of fan blades, characterized in that the equation nxc2x7w3/L=constant is met, where the width of the slits is w, the number of slits in the direction of the axis of rotation is n (n is a positive integer) and the distance in the radial direction between the inner perimeter to the outer perimeter of the annular wall is L, or alternatively the width of the slits, w, and the number of slits in the direction of the axis of rotation, n, are changed according to L so as to satisfy the close condition of said equation.
This arrangement enables the flow rate of air flowing inside the annular wall through the slits to be constant all around the annular wall even when a conventional blower with a rectangular contour is replaced with a blower of the present invention. Thus the P-Q characteristic is improved, and noise is reduced as is the case with a blower with a circular contour, shown in FIG. 12.
By disposing spacers forming and supporting the slits at or near the middle of the four sides of the casing body, the annular plates can be supported as well as weak sections of the annular plates can be reinforced.
Projecting toward the outer perimeter of the annular wall the spacers in the middle of the four sides of the casing body prevents the annular plates from being damaged or deforming under an undue load when a blower is installed.
Tapering the projected sections of the spacers along the axis of rotation increases the workability at the time of installing the blower.
Next, the shape of a blade of a blower fan according to the present invention is described. The present invention provides a blower that sucks air inside the annular wall also through the slits provided therein, wherein the shape of fan blades is improved and in this connection the shape of the housing is further improved.
The present invention improves aerodynamic performance, strength, and mass productivity, thus realizing cost savings.
According to a first aspect of the present invention, which aspect relates to a fan blade shape, a blower that is arranged so that air is sucked inside the annular wall through the slits provided therein is characterized in that a cross-sectional shape obtained by cutting a blade of a fan through the surface of a cylinder concentric with the axis of rotation of the fan is an airfoil and that the shape of the blade near the end thereof is formed to be an airfoil with respect to air flowing in through the slits. The blower is also arranged so that a blade at a section near its end becomes progressively thinner towards the end, and the location which provides the maximum thickness of the airfoil obtained by cutting the fan through the surface of a cylinder concentric with the axis of rotation gradually moves back toward the blade trailing edge side according as the location approaches the end of the blade. The blade advance angle xcex8 is made larger near the end of a blade than in other locations, which angle is set to meet the following equation,
xcex8=tanxe2x88x921(v/u)
where v is the average velocity of air flowing in from outside the annular wall, and u is the peripheral speed of a blade end. The blade advance angle near the end of a blade is set equal to the angle of a slit in the annular wall. The first aspect improves the P-Q characteristic and noise reduction performance.
According to a second aspect of the present invention, which aspect relates to the annular wall associated with a fan, a plurality of annular plates are stacked through spacers in the direction of the axis of rotation, of annular plates being separated from each other, to form the annular wall with slits, and one of the plurality of annular plates which is at the most upstream side of a main air flow produced by the fan is made thicker than the remaining annular plates. This arrangement significantly improves both the P-Q characteristic and the strength of the fan at a high level. In addition, by cutting the upstream-side end surface of the inner periphery of the annular plate on the most upstream side of the main air flow, the periphery becomes thinner, thereby improving blower performance.
According to a third aspect of the present invention, the clearance between the end of a blade and the inner perimeter of the annular wall is wider as it gets farther away from a bearing support. This arrangement has the effect of preventing the dimensions from changing with time and the end of the fan blade from touching the inner perimeter of the annular wall due to initial dimensional variations.
According to a fourth aspect of the present invention, a plurality of annular plates are stacked in a spaced relation from each other through spacers in the direction of the axis of rotation to form an annular wall with slits, and the width of the slits is larger only near the spacers than in other locations. This arrangement cancels the effect of the spacers and improves the P-Q characteristic of a blower. Alternatively, the width of the slits near the spacers is made equal to or smaller than in other locations, thus fully improving the P-Q characteristic and reducing noise.
According to a fifth aspect of the present invention, notches are provided near the spacers in the outer perimeter of the annular plates so as to reduce the radial length of the annular plates. This arrangement cancels the effect of the spacers and improves the P-Q characteristic of the blower.
According to a sixth aspect of the present embodiment, the number of spacers used to stack the annular plates is set at n (n is an integer equal to or larger than five), and at least (nxe2x88x922) of the n spacers are disposed in parallel with each other. This arrangement increases the housing mass productivity, thereby contributing to cost savings. Further, inclining the spacers near four sides of a casing body with respect to the radial direction increases mass productivity and reduces cost while minimizing a deterioration in blower performance. Inclining the spacers in four corners of a casing body with respect to the radial direction is expected to exercise the same effect.
Chamfering or obliquely cutting the outer peripheral ends of the spacers inclined with respect to the radial direction improves blower performance.
According to the final aspect of the present invention, a blower housing molding method for molding a housing of the blower is provided which employs a pair of upper and lower molds for forming the inner surface of the annular wall and a boss, and a pair of slide cores sliding opposite to each other at right angles to the moving direction of the pair of molds, wherein the slits are formed all around the annular wall by said pair of slide cores at a time, and the annular wall with the slits, a base serving as a reference for installing the blower and the boss to which a motor is secured are molded respectively as a single piece. This method can increase mass productivity and reduce noise.